Reciprocating pump system

ABSTRACT

A reciprocating pump assembly includes a linear electric motor having a cylinder, a rotor, and a stator. A multiple of check valves are located near each end of the cylinder. Pairs of check valves are mounted within a T-shaped fitting which permit each fitting to operate alternatively as an inlet and a discharge depending on the direction of the rotor stroke. Another pump assembly utilizes the rotor to separately drive pistons through pushrods.

BACKGROUND OF THE INVENTION

The present invention relates to a pump, and more particularly to alinear electric motor driven reciprocating pump.

Reciprocating pumps/compressors are highly desirable for use in numerousapplications, particularly in environments where liquid flow rate isrelatively low and the required liquid pressure rise is relatively high.For applications requiring less pressure rise and greater flow rate,single stage centrifugal pumps may be favored because of theirsimplicity, low cost and low maintenance requirements. However,reciprocating pumps have a higher thermodynamic efficiency thancentrifugal pumps by as much as 10% to 30%.

One conventional reciprocating pump utilizes a solenoid to drive apiston within a cylinder. When the solenoid is energized the solenoidplunger pushes air out of the discharge. When the solenoid isde-energized a solenoid spring drives the solenoid plunger in anopposite direction drawing air into an inlet. Disadvantageously, asolenoid driven reciprocating pump provides the least force at theextremes of the solenoid plunger travel. The pull on the solenoidplunger increases by the inverse square of the distance between thecenter of the plunger and the center of the magnet such that the forceacross the length of travel is uneven.

A typical air compressor load increases almost linearly as the pistonmoves to compress the air. In a typical pump application the load isgenerally constant along the length of travel. In either application,the force delivered by the solenoid plunger does not match the requiredload, which renders the solenoid pump relatively inefficient.Furthermore, solenoids have relatively limited linear travel whichfurther increases the inherent inefficiencies thereof.

Accordingly, it is desirable to provide a reciprocating pump whichgenerally matches the required load to provide efficient operation.

SUMMARY OF THE INVENTION

A reciprocating pump assembly according to the present inventionincludes a linear electric motor having a cylinder, a rotor, and astator. A multiple of check valves are located near each end of thecylinder. Pairs of check valves are mounted within a T-shaped fittingwhich permit each fitting to operate alternatively as an inlet and adischarge depending on the direction of the rotor stroke.

Operation of the pump assembly utilizes the rotor as a piston within thecylinder. As the rotor is driven toward one endplate, one check valvewithin each fitting is open and one is closed to permit the opposedfittings to alternatively operate as the inlet and the discharge. Whenthe rotor is driven toward the opposite endplate, the check valvesreverse and the fittings reverse operation. The reciprocating pumpassembly provides compression during each stroke of the rotor.

Another embodiment of the pump assembly utilizes the rotor to driveseparate pistons through pushrods. The check valves may be reed valveslocated directly within the piston cylinders to provide other packagingpossibilities.

The present invention therefore provides a reciprocating air compressorwhich generally matches the required load to provide efficientoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

FIG. 1 is a general sectional view of a reciprocating pump assemblyaccording to the present invention;

FIG. 2A is a sectional view of a reciprocating pump assembly in a firstposition;

FIG. 2B is a sectional view of a reciprocating pump assembly in a secondposition;

FIG. 2C is a sectional view of a reciprocating pump assembly in a thirdposition;

FIG. 2D is a sectional view of a reciprocating pump assembly in a fourthposition; and

FIG. 3 is a sectional view of another reciprocating pump assemblyaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a schematic sectional view of a reciprocating pumpassembly 10. The pump assembly 10 generally includes a linear electricmotor 11 having a cylinder 12, a rotor 14, and a stator 16. A firstcheck valve 18, a second check valve 20, a third check valve 22 andfourth check valve 24 are located in pairs near each end of the cylinder12. It should be understood that although the pump assembly 10 isdescribed as a compressor for a gas, other uses such as compressor andpump uses for gases and/or fluids will likewise benefit from the presentinvention.

The cylinder 12 defines a longitudinal axis A. Preferably, the cylinder12 is a tubular member which surrounds the rotor 14. The cylinder 12includes opposed endplates 26, 28 which may be selectively opened toreceive the rotor 14. It should be understood that the cylinder need notbe linear.

The rotor 14 is preferably an inductor rotor which includes an iron core30 with alternating bands of copper 32 and iron 34 mounted about saidiron core 30. It should be understood that other induction rotors withan inner core of ferrous material and an outer layer of conductivematerial may also be used with the present invention.

A seal 36 such as an O-ring is preferably located near each end of therotor 14 to center and seal the rotor within the cylinder 12. The seal36 essentially provides a sliding bearing seal for the rotor 14. Thatis, due to the seals the rotor 14 operates as a piston within thecylinder 12.

Each endplate 26, 28 mounts a pair of check valves 18, 20 and 22, 24within a T-shaped fitting 38, 40. The check valves are each preferablymounted within the T-shaped fitting 38, 40 such that the check valves18, 20 and 22, 24 permit each fitting 38, 40 to operate alternativelysuch that when one check valve is open 18, 22 the opposed check valves20, 24 are closed. The fittings 38, 40 alternate between operation aseither an inlet or a discharge from the cylinder 12. The fittings 38, 40provide communication through a multiple of conduits C1-C4 to transfer afluid medium from a source to a destination.

The stator 16 is mounted about the cylinder 12 to drive the rotor 14 inresponse to a controller 44. The stator 16 includes a multiple ofcooling fins 46 interspersed between a multiple of magnets 48. Themultiple of cooling fins 46 and the multiple of magnets 48 are axiallyretained with a tie-rod 49. The magnets 48 are preferablyelectromagnetic stator windings such as wire wound into coils, however,other magnets may also be utilized by the present invention. Preferably,only three windings (one for each phase) need be used with the presentinvention.

The controller 44 may be a variable speed controller, a switchedreluctance speed controller or other controller which controls apoly-phase power source 50. The controller 44 reverses movement of therotor 14 along the longitudinal axis A by interchanging two of the threephases as generally known. Known chip sets and transistor modules areavailable to provide an induction variable speed drive controller 44 andneed not be fully described herein.

Referring to FIG. 2A, operation of the pump assembly 10 begins with therotor 14 being driven toward one endplate 26 as indicated by arrow X1.In this embodiment, the rotor 14 operates as a piston within thecylinder 12. As the rotor 14 is driven toward endplate 26, the checkvalve 18 located within the T-shaped fitting 38 is open and the checkvalve 20 within the T-shaped fitting 38 is closed such that fitting 38operates as a discharge and fitting 40 operates as an inlet. Fluidwithin the cylinder 12 forward of the rotor 14 discharges through checkvalve 18. Simultaneously therewith, the rotor 14 moves away fromendplate 28 (FIG. 3B) such that the check valve 24 located within theT-shaped fitting 40 is open and the check valve 22 within the T-shapedfitting 40 is closed such that fluid is drawn in behind the rotor 14(relative to Arrow X1). It should be understood that relative positionalterms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,”“behind” and the like are with reference to the figures only and shouldnot be considered otherwise limiting.

Referring to FIG. 3C, the rotor 14 has reached the end of stroke and isadjacent to the endplate 26. Fluid forward of the rotor 14 has beenexpelled through check valve 18 and fluid is drawn in behind the rotor14 through check valve 24. At the end of stroke, the controller 44reverses direction of the rotor 14 (FIG. 3D) and the cycle begins againwith the check valves operating in reverse.

Referring to FIG. 2D, the rotor 14 is driven toward the endplate 28 asindicated by arrow X2. As the rotor 14 is driven toward endplate 28, thecheck valve 18 located within the T-shaped fitting 38 is closed and thecheck valve 20 within the T-shaped fitting 38 is open such that thefitting 38 operates as an inlet and fitting 40 operates as a discharge.Simultaneously therewith, the rotor 14 moves away from endplate 26 suchthat the check valve 24 located within the T-shaped fitting 40 is closedand the check valve 22 within the T-shaped fitting 40 is open such thatair is drawn in behind the rotor 14 (relative to arrow X2). The T-shapedfitting 40 now operates as discharge.

The pump assembly 10 thereby operates to compress fluid as the rotor 14moves in both directions improving the efficiency thereof. The pumpassembly 10 thereby cycles between fittings 38, 40 to provideintake/discharge on each stroke of the rotor 14. The controller 44preferably controls the cycle time of the rotor 14 to provide a desiredoutput.

Referring to FIG. 3, another pump assembly 52 includes a linear electricmotor 54 which drives a first and a second piston 56, 58 within arespective piston cylinder 60, 62. The pistons 56, 58 are respectivelylinked to a rotor 64 of the linear electric motor 54 through pushrods66, 68. In this embodiment the rotor 64 and pistons 56, 58 are separatewhich provides different packaging possibilities. Pairs of check valves70, 72 and 74, 76 are located within the respective piston cylinders 60,62. The check valves 70-76 are preferably reed valves, however otherone-way valves may also be used with this embodiment. A stator 78 ismounted about the rotor 64 to drive the rotor 64 and connected pistons56, 58 in response to a controller 80. As the rotor cycles along axis A,the check valves 70-76 operate generally as described above to providepumping and compression during each cycle of the rotor 64.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from thepresent invention.

The foregoing description is exemplary rather than defined by thelimitations within. Many modifications and variations of the presentinvention are possible in light of the above teachings. The preferredembodiments of this invention have been disclosed, however, one ofordinary skill in the art would recognize that certain modificationswould come within the scope of this invention. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described. For thatreason the following claims should be studied to determine the truescope and content of this invention.

1. A reciprocating pump assembly comprising: a cylinder which defines a longitudinal axis; a first check valve mounted adjacent a first cylinder end; a second check valve mounted adjacent said first cylinder end, said second check valve checking a flow from said cylinder in a direction opposite than said first check valve; a third check valve mounted adjacent a second cylinder end; a fourth check valve mounted adjacent said second cylinder end, said fourth check valve checking a flow from said cylinder in a direction opposite than said third check valve; a rotor mounted within said cylinder; and a stator mounted about said cylinder to reciprocally drive said rotor along said longitudinal axis.
 2. The reciprocating pump assembly as recited in claim 1, wherein said first check valve, said second check valve, said third check valve and said fourth check valve are reed valves.
 3. The reciprocating pump assembly as recited in claim 1, wherein said rotor includes an iron core with alternating bands of copper and iron mounted onto said iron core.
 4. The reciprocating pump assembly as recited in claim 1, further comprising a seal mounted near each end of said rotor.
 5. The reciprocating pump assembly as recited in claim 1, wherein said stator includes a multiple of cooling fins interspersed between a multiple of magnets.
 6. The reciprocating pump assembly as recited in claim 5, further comprising a tie bar which axially retains said multiple of cooling fins and said multiple of magnets.
 7. The reciprocating pump assembly as recited in claim 1, further comprising a controller to control movement of said rotor within said stator.
 8. The reciprocating pump assembly as recited in claim 7, wherein said controller includes a variable speed controller.
 9. The reciprocating pump assembly as recited in claim 7, wherein said controller includes a switched reluctance speed controller.
 10. The reciprocating pump assembly as recited in claim 1, wherein said first check valve and said second check valve are contained within a first fitting and said third check valve and said fourth check valve are contained within a second fitting.
 11. The reciprocating pump assembly as recited in claim 10, wherein said first fitting and said second fitting are T-shaped fittings.
 12. The reciprocating pump assembly as recited in claim 1, wherein said first check valve and said second check valve are opposed within a first fitting and said third check valves and said fourth check valve are opposed within a second fitting.
 13. A reciprocating pump assembly comprising: a cylinder which defines a longitudinal axis; a rotor mounted within said cylinder; a first piston cylinder; a first piston mounted within said first piston cylinder; a first push rod mounted to said first piston and said rotor to drive said first piston along said longitudinal axis in response to movement of said rotor; a first check valve mounted to said first piston cylinder; a second check valve mounted to said first piston cylinder, said second check valve checking a flow from said first piston cylinder in a direction opposite than said first check valve; a second piston cylinder; a second piston mounted within said second piston cylinder; a second push rod mounted to said second piston and said rotor to drive said second piston along said longitudinal axis in response to movement of said rotor; a third check valve mounted to said second piston cylinder; a fourth check valve mounted to said second piston cylinder, said fourth check valve checking a flow from said second piston cylinder in a direction opposite than said third check valve; and a stator mounted about said cylinder to reciprocally drive said rotor along said longitudinal axis.
 14. The reciprocating pump assembly as recited in claim 13, wherein said first check valve and said second check valve are reed valves.
 15. The reciprocating pump assembly as recited in claim 13, wherein said first check valve and said second check valve are located within an end plate of said piston cylinder. 